Hi Larry,
2291 does have a replacement chassis, Comet I think, but that was done years ago. When I acquired the loco,it had a non-functioning Mainline split chassis, so that had to go. The wheels are turned-down Romford ones (all this was done in 1995), which a friend turned down for me, as the current 'RP25' profile wasn't available at the time.
I wasn't doing OO-SF then, though, just what I would call 'normal OO finescale', in other words, bullhead track and kit or hand-built points to match, but with 'normal' clearances.
One aspect of the conversion was that I kept outside bearings on the tender, when I replaced the tender wheelsets (may be Ultrascale).
The lack of lateral movement now causes problems with the OO-SF A5 crossover on 'Bethesda Sidings', in that I am going to have to install a Comet tender chassis with inside bearings, to allow the axles a bit of slop (certainly the centre one). That way, it shouldn't derail when going through the crossover.
None of this has been a problem on my non-SF pointwork on 'Engine Wood' or 'Bleakhouse Road'.